[refactor] Remove inquirer from core; expose create question metadata instead

[kmturley]

Summary

• ManagerLocal.create() imported and drove inquirer directly (inquirer.prompt(...)) - an interactive-CLI/UX dependency baked into what's otherwise an isomorphic browser/server SDK (@open-audio-stack/core, exported for embedding per package.json). Any consumer embedding ManagerLocal for programmatic install/uninstall pulled in inquirer transitively even though they'd never call create(). This is Structural Warning #4 in review.md, and the // TODO Rewrite this code after prototype is proven. comment on create() acknowledged it was never meant to stay long-term.
• Removes create() and inquirer entirely rather than keeping a thinner version - per discussion, interactive prompting belongs in the CLI that uses this package (studiorack-cli), not the package itself.
• Adds src/helpers/createQuestions.ts: createPackageQuestions() (org/package/version - needed first, since the rest depend on them) and createPackageVersionQuestions(type, org, pkg) (name/author/description/license/type/tags/url/donate/audio/image/date/changes - type-appropriate choices, org+pkg-derived url/audio/image defaults). Returns a library-agnostic CreateQuestion shape (name/type/message/default/choices/validate/filter) - not inquirer's own Question type - so core has no prompt-library dependency of any kind, though the shape happens to be close enough that most prompt libraries (inquirer included) can consume it directly.
• ManagerLocal keeps thin delegating instance methods - createQuestions() and createVersionQuestions(org, pkg) - so a CLI can still call these off an existing manager instance, the same calling convention create() had.
• Found and fixed a latent bug while extracting: the removed create() code defaulted a Preset/Project's plugins field to [] (an array), but PresetPlugins/ProjectPlugins are actually { [slug: string]: string } maps, not arrays - this would have produced a wrongly-shaped plugins field in every package scaffolded via create() for those two types. createSave() now defaults files to [] and, for Presets/Projects, plugins to {} (the correct shape) when the caller hasn't set them.
• createQuestions.ts is exported from both index.ts and index-browser.ts - it's pure logic (no fs/node-only APIs), so a browser-based tool could use it too, unlike the rest of ManagerLocal.
• Not included: any change to studiorack-cli, which currently calls manager.create() and will break until it's updated to call createQuestions()/createVersionQuestions() with its own prompt library and pass the answers to createSave(). Per discussion, that follow-up needs this package published first, so it's out of scope here.

This is item 5 of the architectural review in review.md (Structural Warning #4, the inquirer-in-core part specifically).

Test plan

• New tests/helpers/createQuestions.test.ts: org/package slug and version validation, tags filter, url/audio/image default derivation, and type-specific choices per registry type.
• New tests in ManagerLocal.test.ts: createQuestions()/createVersionQuestions() delegate correctly, and createSave()'s new files/plugins defaulting (including the array→object fix) persists correctly to disk.
• npm audit: 0 vulnerabilities after removing inquirer.
• npm run check (format, lint, build, test): 218/218 tests, 18/18 files pass.

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